1. Field of the Invention
The present invention relates to a glass substrate for a magnetic recording medium, and also to a magnetic recording medium using the glass substrate.
2. Description of the Related Art
As a substrate material for a magnetic disk, an aluminum alloy substrate well workable has long been used mainly. However, in a 2.5-inch magnetic disk drive built in a portable personal computer such as a notebook personal computer, there has recently been a tendency to use a strong glass substrate formed of tempered glass or crystallized glass, for example, with the main objective of reduction in size of magnetic particles, improvement in magnetic anisotropy, and prevention of stiction of a magnetic head in response to the recent demands for high-density recording and low flying height of the magnetic head, a NiP layer is formed on the glass substrate by sputtering and thereafter mechanical texturing is applied to the NiP layer.
Thus, in the case of using a glass substrate as the substrate, a NiP layer formed on the glass substrate is generally subjected to texturing. However, in performing the texturing after forming the NiP layer, the glass substrate must be once removed from a chamber of a sputtering device prior to texturing. Further, after texturing, the glass substrate must be returned into the chamber. As a result, a manufacturing cost of a magnetic disk using this glass substrate is increased. Accordingly, a magnetic disk with a magnetic film or the like formed on an untextured glass substrate is also commercially available.
It is therefore an object of the present invention to provide a glass substrate for a magnetic recording medium which can reduce the size of magnetic particles to thereby improve the S/N of a reproducing signal.
It is another object of the present invention to provide a magnetic recording medium using a glass substrate which can improve the S/N of a reproducing signal.
In accordance with an aspect of the present invention, there is provided a glass substrate for a magnetic recording medium, comprising a textured surface having numerous grooves extending in the circumferential direction of the glass substrate; the average roughness of the textured surface being 0.4 nm or less; the number of the grooves being 15 or more per micrometer; the average depth of the grooves being 2 nm or less.
Preferably, the grooves are formed by mechanical texturing using a texturing liquid applied between a texturing tape and the surface of a blank glass substrate rotating, the texturing liquid being an aqueous dispersion of abrasive grains.
In accordance with another aspect of the present invention, there is provided a magnetic recording medium comprising a glass substrate having a textured surface having numerous grooves extending in the circumferential direction of the glass substrate, the average roughness of the textured surface being 0.4 nm or less, the number of the grooves being 15 or more per micrometer, the average depth of the grooves being 2 nm or less; a nonmagnetic metal layer formed on the glass substrate; a base layer formed on the nonmagnetic metal layer; an intermediate layer formed on the base layer; a Co alloy magnetic layer formed on the intermediate layer; and a protective film formed on the Co alloy magnetic layer.
Preferably, the magnetic recording medium further includes a Cr adhering layer interposed between the glass substrate and the nonmagnetic metal layer, and the nonmagnetic metal layer includes a NiP layer. Preferably, the total film thickness of the Cr adhering layer and the nonmagnetic metal layer is 50 nm or less. A metal layer may be embedded in the glass substrate.
In accordance with a further aspect of the present invention, there is provided a manufacturing method for a magnetic recording medium including a glass substrate having a textured surface having numerous grooves extending in the circumferential direction of the glass substrate, the average roughness of the textured surface being 0.4 nm or less, the number of the grooves being 15 or more per micrometer, the average depth of the grooves being 2 nm or less, the manufacturing method comprising the steps of forming a NiP layer on the glass substrate; oxidizing the NiP layer; forming a base layer containing Cr as a main component on the NiP layer oxidized; forming an intermediate layer on the base layer; forming a Co alloy magnetic layer on the intermediate layer; and forming a protective film on the Co alloy magnetic layer.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.